Method and system for controlling radio communications network and radio network controller

ABSTRACT

A method and system are disclosed for controlling radio communications between a terminal (MS, TE) and a communications system (CN, GRAN). A communications connection between the system and the terminal is established by an active radio network controller (RNC) and an active base station (BS). In one embodiment, data communications within the communications connection is directed to the active radio controller by a second radio network controller.

The invention relates to a method and system for controlling a radiocommunications network and a radio network controller. Particularly theinvention relates to the handover procedure in a cellular system. Theinvention can be advantageously applied in broadband radio networks thatoffer fixed network services to their users.

Below it will be described the prior art by first illustrating theoperation of a popular second-generation cellular system and inparticular the handover, or change of active base stations serving amobile station moving in the cellular network's coverage area. Then itwill be disclosed the characteristics of new, third-generation cellularsystems and problems related to prior-art handover solutions.

PRIOR ART

Second-generation Cellular Systems

A terminal of a cellular radio system attempts to choose a base stationso as to operate on said base station's coverage area, or cell.Conventionally, the choice has been based on the measurement of thestrength of the received radio signal in the terminal and base station.For example, in GSM (Global System for Mobile telecommunications) eachbase station transmits a signal on a so-called broadcast control channel(BCCH) and the terminals measure the strengths of the received BCCHsignals and based on that, determine which cell is the most advantageousone as regards the quality of the radio link. Base stations alsotransmit to the terminals information about the BCCH frequencies used inthe neighbouring cells so that the terminals know what frequencies theyhave to listen to in order to find the BCCH transmissions of theneighbouring cells.

FIG. 1 shows a second-generation cellular system that comprises a mobileswitching centre (MSC) belonging to the core network (CN) of thecellular system as well as base station controllers (BSC) and basestations (BS) belonging to the a radio access network (RAN), to whichmobile stations (MS) are linked via radio interface. FIG. 2 shows thecoverage areas C21-C29 of base stations BS21-BS29 of a second-generationcellular system.

In second-generation cellular systems, such as GSM, communicationbetween base stations BS and the core network CN occurs via base stationcontrollers BSC. Usually, one base station controller controls a largenumber of base stations so that when a terminal moves from the area of acell to the area of another cell, the base stations of both the old andthe new cell are connected to the same base station controller. Thus thehandover can be executed in the base station controller. So, in theconventional GSM system, for example, there occur fairly few handoversbetween a base station of a first base station controller and a basestation of a second base station controller. In such a case, theswitching centre has to release the connection with the first basestation controller and establish a new connection with the new basestation controller. Such an event involves a lot of signaling betweenthe base station controllers and the switching centre and as thedistances between the base station controllers and the switching centremay be long there may occur disturbances in the connection during thehandover.

Third-generation Cellular Systems

The prior-art handover arrangement is suitable for the so-calledsecond-generation digital cellular radio systems such as GSM and itsextension DCS1800 (Digital Communications System at 1800 MHz), IS-54(Interim Standard 54), and PDC (Personal Digital Cellular). However, ithas been suggested that in future third-generation digital cellularsystems the service levels offered to the terminals by the cells maydiffer considerably from a cell to another. Proposals forthird-generation systems include UMTS (Universal MobileTelecommunications System) and FPLMTS/IMT-2000 (Future Public LandMobile Telecommunications System/International Mobile Telecommunicationsat 2000 MHz). In these plans cells are categorised according to theirsize and characteristics into pico-, nano-, micro- and macrocells, andan example of the service level is the bit rate. The bit rate is thehighest in picocells and the lowest in macrocells. The cells may overlappartially or completely and there may be different terminals so that notall terminals necessarily are able to utilise all the service levelsoffered by the cells.

FIG. 3 shows a version of a future cellular radio system which is notentirely new compared with the known GSM system but which includes bothknown elements and completely new elements. In current cellular radiosystems the bottleneck that prevents more advanced services from beingoffered to the terminals comprises the radio access network RAN whichincludes the base stations and base station controllers. The corenetwork of a cellular radio system comprises mobile services switchingcentres (MSC), other network elements (in GSM, e.g. SGSN and GGSN, i.e.Serving GPRS Support Node and Gateway GPRS Support node, where GPRSstands for General Packet Radio Service) and the related transmissionsystems. According e.g. to the GSM+ specifications developed from GSMthe core network can also provide new services.

In FIG. 3, the core network of a cellular radio system 30 comprises aGSM+ core network 31 which has three parallel radio access networkslinked to it. Of those, networks 32 and 33 are UMTS radio accessnetworks and network 34 is a GSM+ radio access network. The upper UMTSradio access network 32 is e.g. a commercial radio access network, ownedby a telecommunications operator offering mobile services, which equallyserves all subscribers of said telecommunications operator. The lowerUMTS radio access network 33 is e.g. private and owned e.g. by a companyin whose premises said radio access network operates. Typically thecells of the private radio access network 33 are nano- and/or picocellsin which only terminals of the employees of said company can operate.All three radio access networks may have cells of different sizesoffering different types of services. Additionally, cells of all threeradio access networks 32, 33 and 34 may overlap either entirely or inpart. The bit rate used at a given moment of time depends, among otherthings, on the radio path conditions, characteristics of the servicesused, regional overall capacity of the cellular system and the capacityneeds of other users. The new types of radio access networks mentionedabove are called generic radio access networks (GRAN). Such a networkcan co-operate with different types of fixed core networks CN andespecially with the GPRS network of the GSM system. The generic radioaccess network (GRAN) can be defmed as a set of base stations (BS) andradio network controllers (RNC) that are capable of communicating witheach other using signaling messages. Below, the generic radio accessnetwork will be called in short a radio network GRAN.

The terminal 35 shown in FIG. 3 is preferably a so-called dual-modeterminal that can serve either as a second-generation GSM terminal or asa third-generation UMTS terminal according to what kind of services areavailable at each particular location and what the user's communicationneeds are. It may also be a multimode terminal that can function asterminal of several different communications systems according to needand the services available. Radio access networks and services availableto the user are specified in a subscriber identity module 36 (SIM)connected to the terminal.

FIG. 4 shows in more detail a core network CN of a third-generationcellular system, comprising a switching centre MSC, and a radio networkGRAN connected to the core network. The radio network GRAN comprisesradio network controllers RNC and base stations BS connected to them. Agiven radio network controller RNC and the base stations connected to itare able to offer broadband services while a second radio networkcontroller and base stations connected to it may be able to offer onlyconventional narrowband services but possibly covering a larger area.

FIG. 5 shows coverage areas 51 a-56 a of base stations 51-56 in athird-generation cellular system. As can be seen from FIG. 5, a mobilestation travelling only a short distance can choose from many basestations for the radio link.

New cellular systems can employ a so-called macrodiversity combiningtechnique related to CDMA systems. This means that on the downlink patha terminal receives user data from at least two base stations andcorrespondingly, the user data transmitted by the terminal is receivedby at least two base stations. Then, instead of one, there are two ormore active base stations, or a so-called active set. Usingmacrodiversity combining it is possible to achieve a better quality ofdata communications as momentary fade-outs and disturbances occurring ona given transmission path can be compensated for by means of datatransmitted via a second transmission path.

For selecting an active set an active radio network controllerdetermines, on the basis of the geographic location, for example, acandidate set of base stations, which is a set of the base stations thatare used for measuring general signal strength information using e.g. apilot signal. Below, this candidate set of base stations will be calleda candidate set (CS) in short. In some systems, such as IS-41, separatecandidate base stations are used.

Problems Related to Prior Art

Let us consider the application of a prior-art arrangement to a proposedthird-generation digital cellular system. In third-generation systems,base station handovers and radio network controller handovers are morefrequent than in second-generation systems. One of the reasons behindthis is that the cell sizes may be remarkably small and that there mayoccur need to change the service type e.g. from narrowband to broadbandduring a call.

In accordance with the prior art a handover between radio networkcontrollers would be carried out in such a manner that the user dataconnection between the switching centre and the so-called old activeradio network controller/base station is released and a new connectionis established between the switching centre and the so-called new activeradio network controller/base station. Then the switching centre wouldhave to release/set up many connections, which involves a lot ofsignaling between the switching centre and the radio network controller.Furthermore, there are very many small-sized cells in the area of oneswitching centre, and in broadband applications the amount of user datatransmitted is great. This puts very tight requirements for capacity andspeed on the switching centre hardware, which in large systems cannot bemet at reasonable costs using current technology.

Secondly, known svstems have a problem of how to transmit signaling anddata of the core network CN and signaling of the radio network to aterminal moving in the radio network's area. CN signaling and data arespecifically meant for the terminal and routed via radio networkcontrollers. Radio network signaling may be intended either for theterminal or for the radio network itself so that it can arrange optimaluse of radio resources in the network area. The problem is caused by themoving terminal and its effect on the flow of data in the radionetwork's area.

When using macrodiversity combining the prior art further has theproblem that after a handover between radio network controllers the newradio network controller does not have knowledge of the base stationssuitable for macrodiversity combining so that macrodiversity combiningcannot be used before the new radio network controller has established acandidate set of its own. Therefore, transmission power has to beincreased and only one transmission path can be used temporarily betweenthe system and the terminal. This degrades the quality of communicationsand causes stability problems which must be corrected by constantadjustments.

GENERAL DESCRIPTION OF THE INVENTION

Handovers between active base stations serving a terminal can becategorised as follows:

1. handover between base stations (base station sectors) (intra-RNC HO)

2. handover between radio network controllers inside a generic radionetwork (inter-RNC HO) and

3. handover between generic radio networks (inter-GRAN HO).

The present invention primarily relates to handovers between radionetwork controllers inside a generic radio network (item 2 above).

An object of the present invention is to provide a radio network controlarrangement eliminating above-mentioned disadvantages related to theprior-art arrangements.

One idea of the invention is that a connection is assigned a radionetwork controller through which the user data are directed also whensome other radio network controller is the active radio networkcontroller. This radio network controller assigned to a connection ishere called an anchor controller. If during a connection a base stationconnected to another radio network controller is chosen the active basestation, the user data are directed such that they travel to the activeradio network controller via the anchor controller.

The use of an anchor controller in accordance with the invention bringsconsiderable advantages compared to the prior art. First, the radionetwork topology becomes simple and clear, and the network can be easilyextended and reconfigured. Second, internal traffic events in the radionetwork are handled within the radio network controlled by the anchorftnction so that

a handover between radio network controllers is fast so that it iseasier to meet the requirements for a seamless and lossless handover and

the load of the mobile switching centre MSC remains moderate.

A particularly significant advantage is that the operation of the radionetwork can be made optimal as regards the use of radio resources.Furthermore, when using an anchor controller, data encryption can beperformed in the anchor controller so that encryption keys need not betransmitted during a connection from a radio network controller toanother.

Transmission routing from the anchor controller to the active radionetwork controller can be performed by means of chaining so that allactive radio network controllers used during a call remain transmissionlinks for the duration of the call. Another alternative is to useoptimum routing where radio network controllers between the anchorcontroller and the active radio network controller are bypassed.

Optimum radio network controller routing used in connection with theinvention also brings further advantages. First, the internal signalingload of the radio network remains moderate and signaling can be easilymade fast enough. In addition, the radio network controller's processingrequirements remain reasonable, which makes the solution practical.

A second idea of the invention is that in preparation for a handover alist is compiled in a neighbouring radio network controller of thosebase stations that would constitute the candidate set should saidneighbouring radio network controller be made the active radio networkcontroller. Then the active set AS becomes in conjunction with thehandover the new active set AS′. Said list is here called an externalbase station candidate set. When compiling external candidate sets it isadvantageous to use a boundary base station list (BBSL) that can helpdetermine whether a handover is likely. In addition, so-called intensemonitoring can be used for an external base station set.

The use of an external base station candidate set brings e.g. thefollowing advantages. First, the transmission power change related tothe handover is not great at the interface but the use of power is“smooth”. This results in small total power consumption in the interfacearea and low interference-induced noise level. In addition, the solutionachieves a continuous state as regards the network so that handoverswill not cause deviations from the normal operation and thus a stabilityproblem.

The method according to the invention for controlling radio trafficbetween a terminal and a communications system, which comprises radionetwork controllers and base stations to establish a communicationsconnection between the system and the terminal connected to it andwherein a first radio network controller and second radio networkcontroller serve as active radio network controllers during theconnection, is characterised in that when said second radio networkcontroller is active, the connection is routed to said second radionetwork controller via said first radio network controller.

The communications system according to the invention, which comprisesradio network controllers and base stations to establish acommunications connection between the system and the terminal connectedto it and wherein a first radio network controller and second radionetwork controller serve as active radio network controllers during theconnection, is characterised in that when said second radio networkcontroller is active, the connection is routed to said second radionetwork controller via said first radio network controller.

A communications system radio network controller according to theinvention is characterised in that it comprises means for routingcommunications to another radio network controller during a connection.

A second radio network controller according to the invention ischaracterised in that it comprises means for routing the traffic relatedto a connection between a base station and the second radio networkcontroller.

Preferred embodiments of the invention are disclosed in the sub-claims.

“Active” base station here means a base station that has a user dataconnection with a terminal. “Active” radio network controller here meansa radio network controller with which the active base station is indirect connection so that user data can be transmitted to the activebase station.

“Old” base station and radio network controller mean a base station orradio network controller that was active before the handover, and “new”base station or radio network controller means a base station or radionetwork controller which is active after the handover. It is alsopossible that several radio network controllers are activesimultaneously.

“Handover” here refers to a handover between base stations, radionetwork controllers or radio networks. After the handover it is possiblethat also the old base station/radio network controller remains active.

“User data” here means information usually transmitted on a so-calledtraffic channel between two cellular system users/terminals or between acellular system user/terminal and other terminal via a core network. Itmay be e.g. coded voice data, facsimile data, or picture or text files.“Signaling” refers to communications related to the management of theinternal functions of the communications system.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described in more detail with reference to thepreferred embodiments presented by way of example and to theaccompanying drawing wherein

FIG. 1 shows a second-generation cellular system according to the priorart,

FIG. 2 shows the coverage areas of base stations of a second-generationcellular system according to the prior art,

FIG. 3 shows a third-generation cellular system,

FIG. 4 shows the core network CN of a third-generation cellular systemaccording to the prior art and the radio network GRAN in connection withit,

FIG. 5 shows the coverage areas of base stations of a cellular systemaccording to the prior art,

FIG. 6 shows a flow diagram of the main steps of a method according tothe invention for performing a handover between base stations, radionetwork controllers and radio networks,

FIG. 7 shows a cellular system according to the invention and someembodiments for arranging communications between radio networkcontrollers,

FIG. 8 shows an embodiment of the invention for arranging communicationsbetween radio network controllers of different radio networks by meansof the active protocol of the core network,

FIG. 9 shows a technique according to the invention for performing therouting between radio network controllers by means of chaining,

FIG. 10 shows a technique according to the invention for performing therouting between radio network controllers optimally,

FIG. 11 shows a signaling flow chart of a backward handover in acellular system according to the invention,

FIG. 12 shows a signaling flow chart of a forward handover in a cellularsystem according to the invention,

FIG. 13 shows finctions of radio network controllers before a handoverin a cellular system according to the invention,

FIG. 14 shows functions of radio network controllers after a handover ina cellular system according to the invention,

FIG. 15 shows a signaling diagram of a procedure according to theinvention for adding a new neighbour base station to the active setduring the preparation for a handover,

FIG. 16 shows a signaling diagram of a procedure according to theinvention for removing a neighbour base station from the active setduring the preparation for a handover, and

FIG. 17 shows a signaling flow chart of the execution of a handover in acellular system according to the invention.

FIGS. 1 to 5 were discussed above in connection with the description ofthe prior art. Below, a method according to the invention is describedbriefly with reference to FIG. 6. Then, referring to FIG. 7, a cellularsystem according to the invention and embodiments for transmittingsignaling and user data between two radio network controllers will bedescribed. After that, referring to FIG. 8, it will be disclosed ahandover between a radio network controller in a first radio network anda radio network controller in a second radio network.

Next, referring to FIGS. 9 and 10, it will be disclosed a chained and anoptimised embodiment for setting up routing between radio networkcontrollers. Then, referring to FIGS. 11 and 12, two embodiments will bedescribed for realising optimised routing. After that, two embodimentswill be disclosed for realising macrodiversity combining in a radionetwork according to the invention.

Next, functions of radio network controllers will be described inconjunction with a handover according to the invention with reference toFIGS. 13 and 14. Finally, with reference to FIGS. 13 to 17, it will bedescribed the steps related to a handover in a radio network employingmacrodiversity combining and external candidate set.

The description will be followed by a list of abbreviations used in theFigures and in the description.

Main Steps of a Method According to the Invention

FIG. 6 shows a flow diagram of a method according to the invention for ahandover involving the active base station, active radio networkcontroller and active radio network. First, a static configuration 600of the system is performed comprising the steps below. In step 601, theconnections between a switching centre MSC and the radio networkcontrollers are detected, and in step 602 a GRAN-wide routing table forthe radio network controllers is created. Then, the fixed connections inthe radio network GRAN are established in step 603.

Then it is performed a dynamic configuration 610 of the radio network,comprising connection setup steps and connection steps as follows.First, an anchor controller is specified, step 611, after which a fixedradio network specific connection between a radio network controllerRNC[i] and base stations BS[a(i) . . . k(i)] is established, step 612.Then, radio connections are set up between radio network controllersRNC[i] and mobile station MS [α], and radio links are set up betweenbase stations BS[a(i) . . . c(i)] and mobile station MS[α], step 614.After that, possible handovers within the radio network controller arecarried out in step 615.

If the mobile station receives a strong signal from a base station of anexternal radio network controller, step 620, a new RNC-to-RNC connectionis added, step 621, and the routing is updated and optimised, steps 622and 623. After that, a radio network controller specific fixedconnection is set up between the radio network controller RNC[j] andbase stations BS[a(j) . . . f(j)], step 624. Next, radio connections areset up between the radio network controller RNC[j] and mobile stationMS[α], and radio links are established between base stations BS[a(j) . .. d(j)] and mobile station MS[α], step 625. In step 626, handover isexecuted between radio network controllers RNC[i] and RNC[j].

Both radio network controllers can be active as long as it isadvantageous to use base stations of both radio network controllers. Ifall signal connections between the mobile station and base stations of aradio network controller are terminated, the radio network controllercan be removed from the chain. A radio network controller can also beforced to be removed from the chain when base stations of another radionetwork controller offers better signal connections. In FIG. 6 the radioconnection between the radio network controller RNC[i] and the mobilestation is removed in step 627, and the radio network controllerspecific fixed connection between the radio network controller RNC[i]and base stations BS[a(i) . . . c(i)] is also removed.

FIG. 6 also shows a handover (Inter-GRAN HO) between radio networkcontrollers belonging to two different radio networks GRAN A and GRAN B.In the case of such a handover, the dynamic configuration is repeated inthe new radio network and the same procedures as in the old radionetwork are carried out in the new radio network, steps 631 and 632.

Arranging Communications Between Radio Network Controllers

FIG. 7 shows in closer detail a cellular system's core network CN whichcomprises a switching centre MSC, and a radio network GRAN connected tothe core network. The radio network GRAN comprises radio networkcontrollers aRNC and bRNC and base stations BS1 to BS4 connected tothem. A terminal TE is connected by radio to the system, via the basestations. It should be noted that FIG. 7 shows only a fraction of theusual number of radio network controllers and base stations in a radionetwork.

FIG. 7 illustrates some embodiments of the handover according to theinvention. When setting up a connection, one radio network controller ismade an anchor controller, which in the case depicted by FIG. 7 alsoserves as active radio network controller at the initial stage of theconnection. The anchor controller is here marked aRNC. The Figure showsa situation wherein a radio network controller bRNC is made the activecontroller during the connection.

In an embodiment of the invention the inter-RNC handover signalingmessages, like other radio resource management messages within the radioaccess network as well as the user data, are transmitted encapsulatedvia the core network CN. Then the core network CN serves only as amessage router and link between two radio network controllersfunctioning as tunnelling points. The radio network controllers know howto create and decode these messages as well as how to realise thefunctions requested in them. An advantage of this embodiment is that noseparate physical transmission paths are needed between the radionetwork controllers.

In a second embodiment of the invention there exists a physical linkbetween two radio network controllers, such as a cable or radio networkconnection, for example. Then the handover signaling can be transmitteddirect from a radio network controller to another without participationof the core network CN. From the prior art it is known signaling betweenradio network controllers on protocol layers L1-L2, which, however, doesnot take part in the handover signaling proper.

A third embodiment of the invention relates to a situation wherein thereis no continuous connection between two radio network controllers. Thena solution is applicable where one base station is connected with twonetwork controllers. Thus a base station can actively choose which ofthe two radio network controllers it sends control messages to. Then abase station can also serve as a mediator between radio networkcontrollers so that messages from a radio network controller to anothertravel transparently via the base station in both directions. In thiscase, identification codes are used to distinguish between the messagesand traffic proper between the base station and radio networkcontroller.

FIG. 8 shows a situation wherein it is needed a handover between radionetwork controllers of different radio networks. Then the anchorfunction will not remain in the old radio network but a radio networkcontroller of the new radio network is made the anchor controller. Insuch a handover, the signaling between two radio networks GRAN can becarried out using an actively participating protocol, such as MAP of theGSM system, for instance. MAP will then communicate separately with theanchor radio network controllers of both GRANs and will process thesignaling handover messages related to the handover, like other messagesbetween the core network CN and radio network GRAN.

Routing Between Radio Network Controllers

Let us examine a situation in which a terminal is moving in the coveragearea of a radio network GRAN. The radio network anchor function thenremains in the radio network controller specified for the connection,which means that all messages from the core network to the terminal arefirst taken to the anchor radio network controller which directs themfurther via other radio network controllers to the target radio networkcontroller which delivers them to the terminal via a base station.

Use of the anchor function requires that the anchor-RNC knows howmessages are transmitted to other radio network controllers of the radionetwork GRAN. This may be realised using a GRAN-wide address mechanismsuch that the anchor-RNC knows the routing to other radio networkcontrollers, in which case a so-called fixed routing table is used.Alternatively, the radio network controller is connected to only oneother radio network controller so that messages are always sent forwarduntil a radio network controller detects from the address attached tothe message that the message is addressed to it.

When using such an arrangement, it has to be taken into account that theanchor-RNC can be any one of the radio network's radio networkcontrollers. In a small radio network it is possible to realise anembodiment of the method that employs only one anchor-RNC, common to allterminals, so that no connection-specific anchor-RNC is needed. Then theanchor-RNC functions as master and the other network controllersfunction as slaves. If the radio network controller can be selected, theanchor decision can be made either in the core network CN or in theradio network GRAN. Both the core network and the radio network mustknow which radio network controllers serve as anchors in each of theconnections between the terminal TE and switching centre MSC.

FIGS. 9 and 10 show two embodiments for realising the routing betweenradio network controllers during different stages of connection. FIG. 9shows an arrangement for routing the connection by means of chaining,and FIG. 10 shows an arrangement for routing the connection in anoptimised manner. In FIGS. 9 and 10, circles represent radio networkcontrollers and lines represent connections between radio networkcontrollers, realised e.g. in one of the above-described methodsaccording to the invention. A thick line represents active connectionrouting between a terminal moving in a radio network and the corenetwork CN. Location of the terminal is only represented in the Figureby the radio network controller.

Stages A0 and B0 in FIGS. 9 and 10 represent an initial situation wherethe terminal communicates with the core network through radio networkcontrollers 100 and 900. Stages A1 and B1 represent a situation wherethe terminal is handed over to radio network controllers 111 and 911while the anchor remains in the old radio network controller.

The advantage of the optimised embodiment can be seen in the situationwhere the connection of a terminal is further handed over to either ananchor radio network controller or some other radio network controller.In stages A2 and B2 the next handover is to radio network controller 122and 922. In the chaining method, a new communications link is simplyestablished between the old radio network controller 921 and the newradio network controller 922. In the optimised solution, a newcommunications link is established between the anchor-RNC 120 and thenew radio network controller (122), and the link between the anchor-RNC120 and the old radio network controller 121 is removed.

Stages A3 and B3 illustrate a situation where the connection of theterminal has been handed over back to the anchor-RNC from the initialstate of stages A2 and B2. In the optimised case, the communication linkbetween the old radio network controller 132 and the anchor-RNC 130 isremoved. Since the new radio network controller is the anchor-RNC, nonew communication link needs to be established. In the traditionalchaining method, a loop is made from the anchor-RNC 930 back to theanchor-RNC 930 through all the radio network controllers that theterminal has used during the connection.

Optimised handover can be carried out in two ways depending on whetherit is possible to use the signaling connection with the old radionetwork controller during the handover. In a so-called backward handoverthe old radio network controller is used for signaling during thehandover, and in a so-called forward handover the old radio networkcontroller is not used for signaling during the handover. FIGS. 11 and12 show some ways of carrying out the above-mentioned backward andforward handovers. The description to follow also refers to handoversituations according to FIGS. 9 and 10. Abbreviations used in theFigures are listed in the abbreviation list that follows thedescription.

Backward Handover

FIG. 11 shows by way of example the signaling flow diagram of anoptimised backward handover between radio network controllers. In abackward handover the old connection with the terminal is retained forthe whole duration of the handover so that the radio path parameters ofthe new location can be transmitted to the terminal via the old radionetwork controller 111. In our example the terminal transits from stateA1 shown in FIG. 10 to state A2, i.e. from the old radio networkcontroller 111 to the new radio network controller 112.

An optimised backward handover according to FIG. 11 between radionetwork controllers comprises the following steps:

A terminal TE requiring a handover between base stations sends a messageto the old radio network controller oRNC. When the old radio networkcontroller finds that the new base station required by the terminalbelongs to another radio network controller nRNC, it informs the anchorcontroller aRNC about the request for a backward handover.

Having received the message from the old radio network controller oRNCthe anchor controller aRNC requests the new radio network controllernRNC to reserve fixed and radio connections according to the bearerinformation (BI) for the terminal.

Having received from the new radio network controller an acknowledge forthe reservation of connections under the new radio network controllernRNC the anchor controller aRNC negotiates with the new radio networkcontroller nRNC and they set up the user data transmission link.

Next, the anchor controller aRNC requests the old radio networkcontroller oRNC to send the radio path information of the radio pathreserved under the new radio network controller nRNC to the terminalusing the old, still operational connection.

Having received from the old radio network controller oRNC anacknowledge for the sending of information of the new radio path to theterminal the anchor-RNC requests the new radio network controller tostart transmission to the terminal. Finally, the anchor controller aRNCrequests the old radio network controller oRNC to release the resourcesallocated to the terminal. This can be a forced release after the newbase station set offers better signal connections, or alternatively therelease can be made if none of the base stations of the networkcontroller serves the mobile station.

Forward Handover

FIG. 12 shows by way of example the signaling flow diagram of anoptimised forward handover between radio network controllers. In aforward handover it is assumed that the old connection via the old radionetwork controller oRNC 111 is no longer in use. In the exampleaccording to FIG. 12 a terminal transits from state A1 shown in FIG. 10to state A2, i.e. from the old radio network controller oRNC 111 to thenew radio network controller nRNC 112.

An optimised forward handover according to FIG. 12 between radio networkcontrollers comprises the following steps:

When the terminal and/or new base station nBS find that the terminalneeds a handover and the radio network controller nRNC controlling thenew base station has detected that the old base station belongs toanother radio network controller oRNC, the new radio network controllernRNC sends a message indicating the need for a forward handover to theold base station oRNC either directly (as in FIG. 12) or via the anchorcontroller aRNC.

The old radio network controller oRNC sends a request-acknowledge to thenew radio network controller nRNC and informs the anchor controllerabout the need for a handover. Then the anchor controller aRNC and thenew radio network controller nRNC negotiate and set up a dedicated userdata transmission link.

Having received from the anchor controller aRNC an acknowledge to itshandover request the old radio network controller releases the fixed andradio connections allocated to the terminal. At latest when the newradio network controller has the user data connections from the anchorcontroller aRNC up and operational will the new radio network controllernRNC establish the necessary fixed and radio connections between thebase station and terminal.

Finally, the new radio network controller nRNC sends a message to theanchor controller aRNC indicating that the handover is completed.

Use of Macrodiversity Combining in Radio Network According to Invention

Used with a CDMA-type radio network, which facilitates the combining ofsignals from multiple base stations, or macrodiversity combining, thearrangement according to the invention is characterised by some specialfeatures. Macrodiversity combining employs multiple simultaneousconnections, first, between the terminal and base station sectors and,second, between the terminal and individual base stations. On the uplinkpath the terminal uses one signal and one spread code which is receivedat several base stations. Alternatively, the terminal may use one signalwith several spread codes received at several base stations. The finalsignal is the result of macrodiversity combination. In the downlinkdirection, several base stations transmit one and the same signal spreadusing different spread codes to a terminal that performs themacrodiversity combining. The signal connections that provide sufficientsignal strength at agreed power levels belong to the so-called activeset.

If the active set includes base stations connected with different radionetwork controllers, the macrodiversity combining can be carried outseparately for each radio network controller. Then the final signalcombination is completed only in the anchor-RNC. In another embodimentthe signals are separately routed to the anchor-RNC where themacrodiversity combining proper is carried out. A prerequisite for eachdiversity combining is rough timing information, e.g. with the accuracyof 256 chips, indicating the framework within which bit-level signalcombining can be performed.

Alternatively, macrodiversity combining can be carried out such that thebase stations handle the chip-level timing and make the soft bitdecisions. These bits, represented by a more detailed representationdefined by several bits, are sent to the radio network controller wherethe combining is carried out using the diversity technique.

In a preferred embodiment, packet transmission can be realised in such amanner that same packets are not transmitted via two different basestations. The solution may be such that it is decided on the moment oftransmission of each packet which one of the radio paths is the moreadvantageous one at that moment. The decision may be based e.g. on aprediction on the quality of radio connections, quality calculations orquality measurements. The advantage of macrodiversity combining is thenthat the better-quality radio transmission path branch is used at eachtime. Retransmissions caused by failed packet receptions can be furtherdirected e.g. according to the following selection criteria for theradio transmission path branch:

retransmission uses the radio transmission path branch used in theprevious transmission,

retransmission uses other than the branch used in the previoustransmission or

retransmission uses the branch the quality of which is estimated thebest.

This is to improve the probability of success through retransmission. Anadvantage of this embodiment is e.g. a reduced radio path load as thesame data normally are not transmitted via two branches.

The active set can be limited such that it includes only the basestation connections the base stations of which are connected to the sameradio network controller. However, this embodiment has the disadvantagethat as the terminal crosses the boundary between two radio networkcontrollers, the macrodiversity has to be abandoned momentarily.

In an embodiment in which radio network controllers are connected onlythrough the core network CN, macrodiversity combining is advantageouslyrealised in the nearest radio network controller lest it be necessary totransmit unconnected signals via the CN.

If the radio network controllers are directly connected, macrodiversitycombining according to the invention has two embodiments. The firstembodiment covers the cases wherein macrodiversity combining is carriedout in successive radio network controllers and finally in theanchor-RNC. The second embodiment covers the cases wherein all signalsare separately gathered in the anchor-RNC and macrodiversity combiningis carried out there. This embodiment is advantageous in a solution inwhich the anchor-RNC is the same for all connections in the radionetwork GRAN and the other radio network controllers are just routers.

Mechanisms according to the present invention easily lead to differentradio network topologies. However, in the preferred embodiment the radionetwork is not made topologically complex but it is allowed to utiliseas efficiently as possible the core network to transmit its ownmessages, either passively or actively. As regards the use of radionetwork resources, it is advantageous to retain a sufficient fimctionaldistribution because it is preferable that the radio link layers arelocated as close as possible to the base stations the signals of whichare best detected by the terminal.

Functions According to Invention in Radio Network Controller

According to the invention, a radio network controller advantageouslyhas the following new characteristics.

means for realising anchor functions,

means for storing information on routing to other controllers in theradio network,

means for realising data routing to the core network CN,

means for realising data routing to another radio network controller,

means for communicating with another controller, and

means for carrying out macrodiversity combining by choosing themomentarily strongest signal connection or by combining the signals ofdifferent connections.

FIG. 13 shows radio network controller functions prior to a handover andFIG. 14 shows radio network controller functions immediately after ahandover. In the situation represented by FIGS. 13 and 14, the radionetwork controller RNC0 is the anchor controller and the radio networkcontroller RNC1 is active before the handover and RNC2 is active afterthe handover. In FIGS. 13 and 14, a thick line in the fixed networkrepresents transmission of user data and a thin line a signalingconnection. A thin line between base stations and a terminal indicatesmeasurement operations and a serrated line, or flash symbol, indicatestransmission of user data.

In addition to the anchor RNC functions (ARNCF) the anchor controllerRNC0 realises the user data relay (UDR) to the active radio networkcontroller. In the active radio network controller RNC1 there is amacrodiversity controller (MDC). The active RNC1 also includes amacrodiversity combination point (MDCP) for the uplink direction. Thecorresponding combination point for the downlink direction is located inthe terminal TE. The active radio network controller RNC1 also containsa set controller (SC). For each terminal there is in the active radionetwork controller RNC1 a candidate set (CS) and, as a subset of the CS,an active set (AS).

One or more radio network controllers (RNC2) that control base stationsin the immediate vicinity (handover likely) of the base station set ofthe active radio network controller RNC1 may control an externalcandidate set (ECS). The external candidate set ECS may include one ormore base stations controlled by the radio network controller RNC2. Theradio network controller RNC2 includes an external candidate setcontroller (ECSC) to control the external candidate set.

The anchor controller RNC0 or the active RNC1 (location selectable)includes a so-called set control function (SCF) that monitors the needfor handover between radio network controllers, prepares the necessaryexternal candidate set ECS and executes the handover.

An anchor controller can be established in two alternative manners:

The radio network controller RNC through which the connection wasoriginally set up is chosen the anchor controller. Then, in principle,all radio network controllers may function as the anchor. In practice,this alternative calls for logical RNC-to-RNC connection facilitiesbetween all radio network controllers RNC in the radio network GRAN.

Within a radio network GRAN, all anchors are always established in oneand the same radio network controller, so-called master-RNC, which atthe same time is probably the only radio network controller connectedwith the core network CN. The master-RNC includes the anchor-RNCfunctions (ARNCF). The master-RNC facilitates a star-like topology forthe connections between radio network controllers.

The examples illustrated by FIGS. 13 and 14 are based on a situationwhere the anchor has been selected and one active RNC is connected withit which is not an anchor-RNC.

The anchor controller RNC0 shall have a logical communicationsconnection with both the radio network controller RNC1 and the RNC2. Thephysical realisation of the logical RNC-to-RNC communications connectionbetween the radio network controllers RNC1 and RNC2 may be a directRNC1-RNC2 link or, optionally, the communications between the radionetwork controllers RNC1 and RNC2 can be realised by relaying via theanchor controller RNC0.

In FIG. 13 the set control function SCF is located in the anchorcontroller RNC0 so that a logical connection between radio networkcontrollers RNC1 and RNC2 is not needed. Other logical RNC-to-RNCconnections can be physically realised in the three manners describedabove (via CN, using RNC-to-RNC cable/radio link, or via base stations).A logical RNC-to-RNC communications connection is in principleindependent of the physical implementation. E.g. in optimised routing,where the logical communications connection exists between the-anchorcontroller and the active radio network controller, the physicalconnection can even be relayed via previous active radio networkcontrollers if necessary.

The anchor-RNF function ARNCF comprises tasks as follows:

Setting up logical RNC-to-RNC connections between the anchor controllerand the active radio network controller,

User data relay UDR, i.e. directing the downlink data to radio networkcontroller RNC2 and receiving the uplink data from macrodiversitycombination point MDCP-up/RNC2 of the radio network controller RNC2, and

Setting up, controlling and releasing a logical connection between corenetwork CN and radio network.

The user data relay UDR comprises tasks as follows:

Relaying traffic between a terminal TE and core network CN instead ofbase stations controlled by own radio network controller to anotherradio network controller according to instructions from the anchor-RNCfunction ARNCF.

The user data relay controls the user data stream directly or controlsthe operation of the logical link control LLC. The logical link controlLLC controls the radio connections between the radio network controllerand a terminal. The tasks of the logical link control LLC include errordetection, error correction and retransmission in error situations. Inaddition, the logical link control LLC comprises control for thenecessary buffers and acknowledge windows. The logical link control unitLLC has a generalised meaning; it may terminate the corresponding LLCprotocol of the terminal, but it can alternatively serve as an LLCrelay. In an LLC relay function the locical link control unit mayterminate the messages of the radio network in a normal manner, but itrelays the core network messages (core network data and signaling)further to a defined node of the core network CN. An example of this isrelaying messages between a terminal and core network of the GeneralPacket Radio Service GPRS. In this case the Serving GPRS Support Node(SGSN) would serve as a terminating unit.

The logical link control LLC can be located such that it is always inthe anchor controller. Then there is no need to transmit big LLC bufferswithin the radio network in connection with a handover of an activeradio network controller. Alternatively, the logical link control may belocated always in the active radio network controller, in which case theLLC buffers have to be transferred in conjunction with a handoverbetween radio network controllers. Possible transfer of the logical linkcontrol from a radio network controller to another is carried out underthe control of the user data relay UDR in the anchor controller. Thelocation of the logical link control in the active radio networkcontroller is shown by dashed lines in FIGS. 13 and 14.

The user data relay UDR carries out data relaying also in cases wherethe role of the logical link control is small, e.g. in the so-calledminimum mode, or when the logical link control has no role at all.Possible locations of the logical link control are also determined inpart by the macrodiversity combining used.

Radio network controller managers create or remove, depending on theinternal implementation method, terminal-specific functions (e.g. ECSC,MDC and MDCP) in the radio network controller and direct the signalingmessages to the correct function in the radio network controller.

The macrodiversity combination point MDCP and macrodiversity controllerMDC represent ordinary functions related to the macrodiversityimplementation used. The user data relay UDR is related to inter-RNCcommunications within the radio network. The anchor-RNC function(ARNCF), which is active only during a handover, belongs to thedisclosed anchor-based handover arrangement according to the invention.The set control function SCF, set controller SC and the externalcandidate set controller ECSC belong to the disclosed arrangementaccording to the invention that uses an external candidate set.

In a macrodiversity implementation which comprises on the uplinktransmission path only one transmission in the terminal, themacrodiversity combination point MDCP/up is located in the radio networkcontroller. On the downlink transmission path with multipletransmissions (each base station having its own) the macrodiversitycombination point MDCP/down is located in the terminal.

The macrodiversity combination point MDCP and macrodiversity controllerMDC perform the functions that belong to macrodiversity combiningaccording to the macrodiversity implementation used. The functions addand remove base stations from the internal candidate set and from theactive set.

Furthermore, the macrodiversity controller MDC according to theinvention shall be capable of

indicating to the set controller SC the completed additions or removalsof base stations to and from the active set of base stations,

adding to/removing from the candidate set visible to the terminal thebase stations added to/removed from the external candidate set,

producing for the set controller the necessary radio path qualityreports comparable with the external candidate set controller ECSC, and

indicating on request of the set controller SC to the terminal that anentirely new active set (former external candidate set) has been takeninto use.

The set controller SC carries out tasks as follows:

Checks using the boundary base station list BBSL whether a base stationadded to/removed from the active set belongs to the so-called boundarybase stations of a neighbour radio network controller.

Requests the set control function SCF to realise a creation/removal ofan external candidate set in a neighbour radio network controller and toprovide the necessary information such as the identity of the basestation that triggered the request, the identity of the terminal, etc.

When the external candidate set changes, transmits via themacrodiversity controller MDC to the terminal the information needed bythe terminal in the external candidate set measurement.

Provided that intense monitoring is used, produces and transmitsinformation to the set control function SCF that is comparable withintense monitoring controlled by the external candidate set controllerECSC.

Conveys to the macrodiversity controller MDC the radiotechnicalparameters of the external base station set that is about to becomeactive. The macrodiversity controller MDC sends them further to theterminal like the parameters it produced itself.

On request of the set control function SCF, terminates the operation ofa terminal in its own radio network controller RNC1 or, alternatively,converts the active set of its own radio network controller to theexternal candidate set of the new active radio network controller RNC2.

The set control function SCF comprises tasks as follows:

On request of the set controller SC, allows/forbids, possiblynegotiating with, say, the target radio network controller, the creationof an external candidate set ECS.

Requests that a neighbour radio network controller create an externalcandidate set for a certain terminal, transmitting the information (say,base station identity) produced by the active radio network controllerto the neighbour radio network controller RNC2.

When creating or modifying an external base station set transmits to theset controller SC the data needed by the terminal in the measurement.

Receives the connection quality reports of the set controller SC andexternal candidate set controller and makes a handover decision based onthem.

Decides on a handover to a. neighbour radio network controller or onintense monitoring.

If intense monitoring is possible, requests the external candidate setcontroller ECSC to start intense monitoring. Requests from themacrodiversity controller the data required for intense monitoring andsends them to the external candidate set controller. Requests themacrodiversity controller to produce data comparable with the intensemonitoring data produced by the external candidate set controller ECSCif said data differ from normal reference data. Receives the intensemonitoring results from the external candidate set controller ECSC andcompares them with the quality data received from the set controller SC.

Indicates to the external candidate set controller ECSC that thehandover has been completed and receives the radiotechnical parametersof the active external base station set of the external candidate setcontroller ECSC and sends them further to the set controller SC.

Indicates to the anchor-RNC function ARNCF that the handover has beencompleted between the two radio network controllers.

When the base station set of the radio network controller RNC2 hasbecome the active set, requests the set controller SC/RNC1 of the oldradio network controller RNC1 to terminate operation and to remove therest of the functions related to the terminal from the radio networkcontroller RNC1 or, alternatively, convert the radio network controllerRNC1 into an external candidate set controller for the radio networkcontroller RNC2.

The external candidate set controller ECSC has tasks as follows:

When starting for a given terminal it creates for the base stationBS/RNC1, which triggered the preparation, a suitable external candidateset ECS based e.g. on geographic and/or propagation technical locationdata and, when the external candidate set ECS exists, updates itconstantly according to the base stations added to/removed from theactive set.

Conveys to the set control function SCF the data required for theexternal candidate set ECS measurement at the terminal.

In intense monitoring, on the basis of the terminal-specific informationproduced by the set control function, sets up in the radio networkcontroller RNC2 the functions that are needed in the uplink qualitysampling and reports the results of the sampling to the set controlfunction SCF.

As handover starts, sends the radiotechnical parameters of the externalbase station set becoming active to the set control function SCF. Startsin the radio network controller RNC2 the uplink macrodiversitycontroller MDC/RNC2 and the macrodiversity combination pointMDCP-up/RNC2 needed in the active radio network controller, using theexternal candidate set as the initial state for the new active set. Atthe same time establishes the fixed and radio connections needed by theactive set.

Execution of Handover Between Radio Network Controllers

Let us consider the execution of a handover between radio networkcontrollers in the exemplary situation depicted by FIGS. 13 and 14. Twophases can be discerned in the handover between radio networkcontrollers:

inter-RNC handover preparation phase and

inter-RNC handover execution phase.

Handover Preparation Phase

The following example of the preparation phase assumes that the setcontrol function SCF is in the anchor controller RNC0, so a connectionbetween radio network controllers RNC1 and RNC2 is not needed. Thepreparation phase is the same in the uplink and downlink directions.

In the situation depicted in FIGS. 13 and 14 the handover preparationcomprises the following steps:

First, the radio network controller RNC1 adds a base station to theactive set AS. The signaling flow diagram in FIG. 15 shows one method ofadding a base station to the active set. Then the set controller SC/RNC1detects on the basis of the boundary base station list BBSL that a basestation has been added to the active set which is located in theimmediate vicinity of the base stations controlled by a neighbour radionetwork controller RNC2. The set controller SC/RNC1 sends a messageabout this to the set control function SCF. If this is the first suchbase station, the set control function SCF requests that an externalcandidate set controller ECSC be started in the neighbour radio networkcontroller RNC2.

Next the radio network controller RNC2 starts the external candidate setcontroller ECSC for the terminal. Based e.g. on the geographic locationdata the external candidate set controller ECSC determines a suitableexternal candidate set ECS for the terminal and sends information aboutthe base stations belonging to the external candidate set to the radionetwork controller RNC1 via the set control function SCF. Alternatively,if there is a direct signaling connection between the radio networkcontrollers RNC1 and RNC2, this can be done direct to-the set controllerSC/RNC1. The set controller SC/RNC1 adds the external candidate set ECSto the set of base stations to be measured at the terminal. This is donecontrolled by the macrodiversity controller MDC/RNC1 as in the case ofan internal candidate set.

After that the terminal uses e.g. pilot signals to perform usualmeasurements for the base station set that includes the candidate set CSand the external candidate set ECS. In this example it is assumed thatthe terminal makes a decision or proposition for transferring basestations between the active set and the candidate set, and the transfercan be carried out by the macrodiversity combination point MDCP andmacrodiversity controller MDC. The set controller SC/RNC1 is informedabout the transfer. When the macrodiversity controller MDC/RNC1 detectsthe request of transferring a base station belonging to an externalcandidate set ECS to the active set, the request is transmitted to theset controller SC/RNC1 to be further considered or to be executed.

If the only boundary base station toward the radio network controllerRNC2 is removed from the active set, the set controller SC/RNC1, havingdetected the situation, removes the external candidate set controllerECSC from the radio network controller RNC2 by sending a removal requestto the set control function SCF/RNC0, FIG. 16. The set control functionSCF/RNC then conveys the request to the radio network controller RNC2which removes the external candidate set controller ECSC. The procedurethen starts over again. Otherwise the set controller (SC/RNC1) requestsfor external candidate set update in the radio network controller RNC2.

If the set control function SCF finds that a base station/base stationscontrolled by the radio network controller RNC2 give(s) a better signal,the set control function SCF may alternatively order a handover betweenradio network controllers RNC1 and RNC2 or only start optional intensemonitoring in the radio network controller RNC2.

In intense monitoring, a preprocess MDCP′ like the macrodiversitycombination point is set up in the radio network controller RNC2 for theuplink transmission path, and said preprocess once in a while receivesdata from the terminal but does not itself transmit data further butonly the connection quality report to the set control function SCF.

Having found on the basis of measurements or intense monitoring that ahandover is necessary to base station(s) controlled by the radio networkcontroller RNC2, the set control function SCF starts the execution phaseof a handover between radio network controller RNC1 and radio networkcontroller RNC2. ps Handover Execution Phase

An inter-RNC handover can be carried out as follows:

The active set is completely transferred to the new radio networkcontroller RNC2. Thus only one radio network controller is active at atime. In the handover execution phase the external candidate set ECS2 ofthe radio network controller RNC2 completely becomes the terminal'sactive set AS, and the active set AS1 and candidate set CS1 of the radionetwork controller RNC1 are removed. Optionally, the active set AS ofthe radio network controller RNC1 may remain as candidate set ECS1. Thisarrangement avoids the problem of RNC synchronisation found inhierarchic combining.

In hierarchic combining, each radio network controller has an active setof its own. All active radio network controllers perform their owncombining for the data in the uplink direction. Final uplink combiningcan be carried out in radio network controller RNC0. Then it is notnecessary to establish a macrodiversity controller proper MDC/RNC0 inthe radio network controller RNC0 or functions equivalent to amacrodiversity combination point MDCP-up/RNC0, if the combination pointsof the active radio network controllers are able to preprocess the finalresult for fixed transmission in such a manner that final combining iseasy to perform in the radio network controller RNC0. Alternatively, oneof the active radio network controllers may serve as a so-calledcombination anchor, combining the user data of the other active radionetwork controllers prior to the transmission to the radio networkcontroller RNC0. The user data relay UDR/RNC0 has to duplicate thedownlink user data for the downlink connection combined in the terminal.Additionally, the base stations of the active sets of the differentradio network controllers must be synchronised as required by the CDMAmethod used. Hierarchic combining may comprise several hierarchy levels.

A combination of the alternatives described above is used e.g. in such amanner that the downlink direction employs complete transfer of activeset and the uplink direction employs hierarchic combining. Then in thedownlink direction user data are transmitted via the previous active setuntil measurements show that the new base station set is better. Thenthe downlink data will be transmitted via the new set. By means of thissolution, the advantages of hierarchic combining are retained in theuplink direction but data duplicating is avoided in the downlinkdirection.

Following example of the execution phase of an inter-RNC handover isbased on the complete transfer of the active set both in the uplink andin the downlink directions (alternative 1). The execution phase exampleassumes that the set control function SCF is located in the anchorcontroller RNC0 so that no logical RNC-to-RNC connection is neededbetween the radio network controllers RNC1 and RNC2. The execution phaseexample is based on the use of macrodiversity in a generic CDMA system.The example is illustrated by the message flow diagram in FIG. 17.

In the example discussed here the handover execution comprises thefollowing steps after the set control function (SCF) has made thehandover decision.

First, the anchor function ARNCF of the anchor controller RNC0 sets up alogical RNC-to-RNC connection between the anchor controller RNC0 and thenew active radio network controller RNC2. Then the set control functionSCF informs the radio network controller RNC2 about the execution of thehandover. The external candidate set controller ECSC sends to the setcontrol function SCF or, alternatively, direct to the old set controllerSC/RNC1 the radiotechnical parameters of the active-to-be base stationset to be further transmitted to the terminal. Internal operation of theradio network controller RNC2 is mostly the same as in conjunction withthe set-up of a normal call with the difference that the externalcandidate set is immediately made the final active set. Instead of anexternal candidate set, a set controller SC/RNC2, macrodiversitycontroller MDC/RNC2 and macrodiversity combination point MDCP/RNC2 areestablished for the uplink direction. Controlled by the radio networkcontroller RNC2 it is reserved or created terminal-specific fixedbearers needed for user data transmission between the radio networkcontrollers and the base stations in the active set as well as radiobearers between base stations and the terminal in manners used in theradio network unless such connections have already been completelycreated in intense monitoring of the preparation phase.

On request of the set control function SCF the user data relay UDR inthe anchor-RNC function ARNCF modifies its operation as follows. Theuser data relay UDR prepares to receive the uplink user data from themacrodiversity combination point MDCP-up/RNC2 of the radio networkcontroller RNC2. The user data relay UDR directs the downlink user dataalso to the radio network controller RNC2.

Next, the set control function SCF/RNC2 sends to the set controllerSC/RNC1 of the radio network controller RNC1 the parameters (such as thetime reference and the scrambling and/or spreading code used) of thepilot signals of the base stations in the active set of the radionetwork controller RNC2. The set controller SC/RNC1 in the radio networkcontroller RNC1 sends to the terminal the parameters of the new activeset.

Then the macrodiversity combination point MDCP/RNC2 in the radio networkcontroller RNC2 starts transmission with the new active set AS/RNC2.This is acknowledged to the anchor-RNC function ARNCF via the setcontrol function SCF.

Finally, the anchor function ARNCF may request the radio networkcontroller RNC1 to remove the terminal's set controller SC/RNC1,macrodiversity controller MDC/RNC1 and macrodiversity combination pointMDCP/RNC1 as well as to release the terminal-specific fixed bearersbetween the radio network controllers and base stations and possibleremaining radio path reservations. Alternatively, the anchor controllermay request the radio network controller RNC1 to turn the active set ofthe radio network controller RNC1 into an external candidate set ECS.This having been acknowledged, the inter-RNC handover is completed.

In the examples discussed above it is assumed that the frequency of theexternal candidate set ECS complies with re-use 1, typical of a CDMAsystem, so that the external candidate set has the same frequency as thecandidate set proper. It is however possible to establish an externalcandidate set at another frequency. Then, the active set AS of only onecandidate set can be in use. Even if macrodiversity combining were notan advantageous solution between different frequencies, this embodimentstill facilitates the change from candidate set AS to new candidate setAS′ in accordance with the principles set forth above.

Applications of Invention

The present invention can be used in connection with a great number ofapplications. These include e.g. database search services, datadownloading, video conferencing, “on demand” data purchases from acommunications network, use of world wide web services in the Internetincluding web browsing etc.

The embodiments discussed above are naturally exemplary and do not limitthe invention. For example, the terminal may comprise a mobile station,portable terminal or a fixed terminal, such as the terminal of acordless subscriber connection.

Particularly it should be noted that the creation of an externalcandidate set for an inter-RNC handover can be carried out independentlyof whether data communications will be routed to the new active basestation via another radio network controller, such as an anchorcontroller.

The steps of the above-described method according to the invention canalso be carried out in an order other than that given above and somesteps may be skipped as unnecessary.

Above it was discussed embodiments wherein the radio network employs theCDMA system. However, it should be noted that the present invention isin no way limited to the CDMA system but it can be utilised in othersystems as well, such as the TDMA system, for example.

LIST OF ABBREVIATIONS USED IN FIGURES AND DESCRIPTION

CN Core Network

GRAN Generic Radio Access Network

TDMA Time Division Multiple Acess

CDMA Code Division Multiple Acess

TE Terminal Equipment

BS Base Station

nBS new Base Station

oBS old Base Station

BSC Base Station Controller

RNC Radio Network Controller

nRNC new Radio Network Controller

oRNC old Radio Network Controller

aRNC anchor Radio Network Controller

aRNCF anchor Radio Network Controller Function

bRNC active Radio Network Controller which is not anchor RNC

UDR User Data Relay

CS Candidate Set

AS Active Set

ECS External Candidate Set

ECSC External Candidate Set Controller

MDC Macrodiversity Controller

SC Set Controller

SCF Set Control Function

BBSL Boundary Base Station List

MDCP Macrodiversity Combination Point

RI Radiopath Information

BI Bearer Information

ID Identity

HO HandOver

ack acknowledge

up uplink

down downlink

req request

resp response

What is claimed is:
 1. A method for controlling radio communicationbetween a terminal (MS, TE) and a communications system (CN, GRAN) in acommunications system, the communication being with a spread codesignal, the method comprising steps of establishing a communicationsconnection between the system and the terminal via an active radionetwork controller (RNC) and active base station (BS), directing thecommunications connection to said active radio network controller via asecond radio network controller (621-628), and employing in thecommunications system macrodiversity combining so that a spread codesignal combination is carried out in a chain formed by radio networkcontrollers serving as transmission links; wherein prior to a handoverbetween radio network controllers, an external candidate set isestablished and a candidate set of a new active radio network controlleris established on the basis of said external candidate set; and whereina handover between radio network controllers comprises a preparationphase and execution phase.
 2. The method of claim 1, wherein saidpreparation phase includes a step for adding a base station to theactive set.
 3. The method of claim 1, wherein said execution phaseincludes steps for changing the active radio network controller and theactive base station set.
 4. The method of claim 1, wherein saidexecution phase includes steps for keeping at least two radio networkcontrollers and their base station sets active.
 5. The method of claim1, wherein the active radio network controller and base station set arecompletely transferred.